1. Field of the Invention
The present invention relates to an inductive write head combined with a magnetoresistive (MR) read head and, more particularly, to a combined head with improved topography in which pads and leads are planar, thereby eliminating shorts or opens in the structure due to steps.
2. Description of the Related Art
Typical mass storage devices store information on spinning magnetic disks, the information being recorded by transitions in magnetic flux on the magnetic surface of the disk. In particular, the data is recorded in a plurality of tracks, with each track being a selected radial distance from the center of the disk. A read/write head is positioned in close proximity to the disk surface and is held in place by an arm. Under control of the systems processor unit, the arm can move the read/write head to the appropriate track where data is recorded that it can be read or written.
A magnetic disk drive includes a magnetic head in a transducing relationship with a surface of the magnetic disk. When the disk is rotated, the magnetic head is supported on a thin cushion of air. The magnetic head may then be employed for writing information to multiple circular tracks on the surface of the disk, as well as for reading information therefrom. Processing circuitry exchanges signals, representing such information, with the head, provides motor drive signals for rotating the magnetic disk, and provides control signals for moving the head to various tracks. The magnetic head is comprises two components, an inductive write head and a read head.
An inductive write head includes a coil layer embedded in an insulation layer between first and second pole piece layers. A gap is formed between the first and second pole piece layers by a gap layer at an air bearing surface (ABS) of the write head. The pole piece layers are connected at a back gap. Current conducted through the coil layer produces a magnetic field in the pole pieces. The magnetic field fringes across the gap at the ABS for the purpose of writing the aforementioned data in tracks on the rotating disk or longitudinal tracks on a moving magnetic tape.
The second part of the head is the read portion. One type of head is the magnetoresistive (MR) head that utilizes direct magnetic flux sensing as a means of readback. The MR head includes a magnetoresistive sensor that detects magnetic field signals through resistance changes of a magnetoresistive material. In applying MR sensors to magnetic recording, many difficulties must be addressed including magnetic behaviors of the sensors that are appropriate for the recording environment and fabrication of the sensors.
For efficient read/write operations, the inductive write head should be placed in close proximity to the MR sensor. One type of read/write head is called a "piggy back" head, where the inductive head and the MR sensor positioned adjacent to each other. For closer placement of the components, a merged head is used. In the merged head, some components of the inductive head are shared with the MR head. Still another type of head places the MR read sensor at the center of the write gap between the pole tips. The problem with this design is intense magnetic field perturbations at every write cycle may aggravate instability problems of the MR sensor. Further, the pole tips are wide at the ABS in order to provide proper shielding for the MR sensor resulting in decreased track width density.
During fabrication of these heads, each of the layers is fabricated one on top of the next. The first device to be fabricated is the MR head and then the inductive head is fabricated. The MR head comprises a sensor located between first and second gap layers and the gap layers are located between first and second shield layers. To fabricate the MR head, the first shield layer is formed on a substrate with undercoat therebetween, the first gap layer is fabricated next, the MR sensor is next, next is the second gap layer and finally is the second shield layer. The inductive write head is then fabricated on top of the MR head. Fabrication of the inductive head includes a coil layer located between insulation layers with the insulation layers being between first and second pole piece layers. For the "piggy back" head, the first pole piece layer is formed on top of the second shield layer of the MR head. For a merged head, the second shield layer is the same as the first pole piece layer (performs a double function).
One disadvantage of the layered structures described above is the uneven or "stepped" topography resulting from the layering process. Most commonly, each of the layers differ in width, such that as the layers are formed on top of one another, steps form near the edges. As multiple layers are formed, multiple steps may be formed. These steps are a common area of failure causing shorts and opens for the lead layers that connect the MR sensor and coil contact points pads to the outer edge of the head. Another problem is if the diameter of the coil is greater than the previous layers, portions of the coil then are formed on multiple layers or steps, which could lead to shorts or opens in the coil itself.
It is desirable to provide a substantially even surface below the inductive coil. This is accomplished by adding material, such as an insulation layer or hard bake resist around the sides of a narrow layer to widen the layer under the coil area. A chemical mechanical polish (CMP) may then be done to eliminate the step and create a planar surface for the next layer. This solution introduces additional steps to the manufacturing process and makes excessive regions of hard bake resist.
Another method of planarization is to extend the layers under the coil to form planar surfaces for each subsequent layer. This makes layers that are unnecessarily large and not optimized. Extending the area of the pole pieces increases the risk of shorting between the lower pole piece and the shielding layer of the MR leads in the merged head. Additionally, extending the layers also extends the leads, which then increase lead resistance and the possibility of shorting between the leads and the shield layers. It is desirable to reduce the length and total area of the MR leads.
While prior art solutions, as indicated above, have described planar regions under the coil above the second shield layer (S2) of the MR head, the remainder of the head is not planarized. This creates shorts or opens in the leads that connect the pads at the outer edge to the MR sensor and coil contacts. Excessive topography for the leads can result in shorting paths around the outside edges of the hard baked regions. Additionally, these leads and pads are separated from the substrate only by the undercoat increasing the chance of capacitance coupling between the conducting undercoat layer and the leads and pads.
From the above it becomes apparent that the prior art combination inductive write head with MR read head results in devices that create pseudo planar surfaces with additional problems or do not provide planarization over the entire head structure. What is needed then is a combination read/write head that planarizes the head to eliminate shorts or opens due to underpass features, S1 shield or S2 shield. Ideally, the improved head should reduce the amount of hard baked resist and optimize the width of the shield layers.